BRL CAD is a 3D modeling, CSG (constructive solid geometry) system. Developed by Mike Muuss, it is a complete package with tools for signal and image processing. At the same time, there is support for scripting and frame buffer as well. The vast number of tools built in mean you won’t have to install other programs for editing.
The program also has its own tools for geometric analysis, graphics rendering (with ray trace support) and an interactive geometry editor. Because it has a lot of features, the program can be used for creating different types of graphics, and it can also be used for electromagnetic and ballistic analyses as well.
If you are familiar with CAD, this one should not be too difficult to learn. In fact it is easier to learn as the package contains all the utilities, tools, libraries you will need to manipulate files and data, ray trace and create objects.
What sets BRL CAD apart from other 3D modelers is that it relies on Constructive Solid Geometry instead of Boundary Representation. Because of this feature, the software is capable of simulating physical phenomena.
With this program you can make geometric models with customizable tools. To make things easier for you, its libraries each have a specific purpose like image handling, geometry ray tracing, editing, and creating and so on. The software also has plenty of utilities and tools for converting images, interrogation and geometric conversion.
There are many free CAD programs out there, but few are as comprehensive as this one. If you are looking for a solid well rounded 3D modeling software, this is a pretty good option.
BRL-CAD Official Website